The above-listed applications are commonly assigned with the present invention and are incorporated herein by reference as if reproduced herein in their entirety.
The present invention is directed, in general, to multimedia systems and, more specifically, to a system for communicating a private network signalling message over a packet network, and bridges for communicating a Media Access Control (xe2x80x9cMACxe2x80x9d) layer frame over an isochronous channel and for communicating an isochronous signalling frame over a nonisochronous network.
Currently, xe2x80x9cInformation superhighwayxe2x80x9d and xe2x80x9cmultimediaxe2x80x9d are probably the most often spoken and least often understood aspects of a coming revolution in data communication. Although issues specific to an information superhighway are beyond the scope of the present discussion, interactive multimedia systems are very much within the present scope.
An interactive multimedia system is broadly defined as a system capable of processing, storing, communicating and coordinating data pertaining to visual information, aural information and other information. Visual information is generally divided into still picture or graphics and full motion video or animation categories. In the vernacular of those involved in multimedia, such visual information is generically referred to as xe2x80x9cvideo.xe2x80x9d Aural information is generally divided into speech and non-speech categories and is generically referred to as xe2x80x9cvoice.xe2x80x9d xe2x80x9cOther informationxe2x80x9d is directed primarily to computer data, often organized in files and records, and perhaps constituting textual and graphical data. Such computer data are generally referred to as xe2x80x9cdata.xe2x80x9d
To date, multimedia has, for the most part, been limited to stand-alone computer systems or computer systems linked together in a local area network (xe2x80x9cLANxe2x80x9d). While such isolated systems have proven popular and entertaining, the true value of multimedia will become apparent only when multimedia-capable wide area networks (xe2x80x9cWANsxe2x80x9d) and protocol systems are developed, standardized and installed that permit truly interactive multimedia. Such multimedia systems will allow long distance communication of useful quantities of coordinated voice, video and data, providing, in effect, a multimedia extension to the voice-only services of the ubiquitous telephone network.
Defining the structure and operation of an interactive multimedia system is a critical first step in the development of such system. Accordingly, before entering into a discussion herein of more specific design issues, it is important to discuss more general questions that need to be resolved concerning design objectives of the system as a whole and some generally agreed-upon answers and specifications.
Interactive multimedia may be thought of as an electronic approximation of the paradigm of interactive group discussion. It involves the interactive exchange of voice, video and data between two or more people through an electronic medium in real time. Because of its interactive and real-time nature, there are some stringent requirements and required services not normally associated with multimedia retrieval systems. Some of the more obvious examples of those requirements and services include latency (transmission delay), conferencing, availability (xe2x80x9cup-timexe2x80x9d) and WAN interoperability.
The evolution of existing private branch exchange (xe2x80x9cPBXxe2x80x9d) and LAN topologies towards a composite interactive multimedia system based upon client/server architectures and isochronous networks is a natural trend. However, to merge the disparate mediums of voice, video and data successfully into a cohesive network requires that three fundamental integration issues be defined and resolved. The first of the fundamental integration issues is quality of service (xe2x80x9cQoSxe2x80x9d). QoS is defined as the effective communication bandwidth, services and media quality coupling of separate equipment or xe2x80x9cterminalsxe2x80x9d together and the availability (xe2x80x9cup-timexe2x80x9d) of the same. QoS parameters are divided into four groups: 1) terminal QoS, 2) network QoS, 3) system QoS, and 4) availability requirements. Thus, QoS parameters must be defined for both terminal equipment (xe2x80x9cTExe2x80x9d) and network equipment (xe2x80x9cNExe2x80x9d) governing the communication of data between the TE. System QoS is derived from a combination of terminal and network QoS. The suggested values for QoS parameters are considered to be a practical compromise between required service quality, technology and cost. See, Multimedia Communications Forum (xe2x80x9cMMCFxe2x80x9d) Working Document xe2x80x9cArchitecture and Network QoSxe2x80x9d, ARCH/QOS/94-001, Rev. 1.7, MMCF, (September 1994) and ITU-T Recommendation I.350 xe2x80x9cGeneral Aspects of Quality of Service and Network Performance in Digital Networksxe2x80x9d, including Integrated Services Digital Networks (xe2x80x9cISDNsxe2x80x9d), (1993). The following Table I summarizes some suggested parameters for terminal QoS.
Network QoS parameter requirements consist of those parts of the system that are between two TE endpoints. This includes a portion of the TE itself, the private network (if required), and the public network (if required). Some of the requirements imposed upon the network QoS are a result of the terminal QoS parameters. The following Table II summarizes the network QoS requirements.
The system QoS encompasses the terminal and network elements. The particular value critical to the system is the intramedia latency. The following Table III summarizes this value that is the sum of the terminal and network values for the same parameter.
The system QoS parameter of Intramedia Latency is the sum of twice the TE and the NE latency. Intramedia Latency parameter value is bounded by voice requirements since latent delay is more readily perceived by the ear than the eye. However, the delay itself is typically a function of video since it is the component requiring the most time for encoding and decoding.
Availability (xe2x80x9cup-timexe2x80x9d) includes several aspects. In particular, the network elements have very strict requirements. These requirements are typical of private branch exchanges (xe2x80x9cPBXsxe2x80x9d) and other private network voice equipment, but are very atypical of Legacy LANS. Most LANs are susceptible to power-losses, single points of failure, and errant TE. An interactive multimedia system must closely follow the availability requirements of the legacy voice systems. The following Table IV summarizes Availability QoS parameters.
The availability requirements are defined solely within the context of the private network. Additional availability parameters are discussed in G.821, See also. MMCF Working Document xe2x80x9cArchitecture and Network QOSxe2x80x9d, ARCH/QOS/94-001, Rev. 1.7, Multimedia Communications Forum, Inc., (September 1994) and TR-TSY-000499, Transport Systems Generic Requirements (TSGR): Common Requirements, Bellcore Technical Reference, Issue 3, (December 1989).
The second of the fundamental integration issues is network services. Network services include transport services, connection management and feature management. Multimedia communication involves the transmission of data having more varied characteristics than video, voice or data in isolation. Therefore, the manner in which the network transports and, manages the flow of video, voice and data is critical to the efficiency, flexibility and overall effectiveness of the network.
Transport services can be categorized into three groups: 1) packet, 2) circuit and 3) cell. The following. Table V summarizes different aspects of each of these transport services.
Interactive multimedia requires the usage of an isochronous network because of the QoS requirements for voice and video. While it is possible to construct a packet network with sufficient bandwidth, buffering and intelligence to accommodate synchronous traffic it is considered to be prohibitively expensive and unnecessary. Nevertheless, both the LAN, PBX and WAN require interoperability.
At some point it is expected that the entire private network infrastructure will employ ATM. This will transpire upon the occurrence of several events. First, WANs must adapt to support ATM Points-of-Presence (xe2x80x9cPOPsxe2x80x9d). Second, the telephone must disappear from the premise (replaced by an ATM audio device). Third, packet-based LAN TE must become ATM TE. Fourth, phantom power must be supported to the ATM TE (for availability purposes). Fifth, an 8kHz synchronous clock must be supported and managed by all ATM equipment. Finally, the price of ATM TE and NE must approach that of Ethernet(copyright), ISDN, and isoEthernet(copyright) equipment.
Regardless of the interim private network infrastructure, ATM is the only backbone solution for the private network. It is the only scalable switching architecture that can transport packet and isochronous data. Furthermore, because its is deployed as a backbone, the aforementioned issues do not apply.
Connection management is the process employed by the private and public network routing functions. Because packet routing is a well established and defined process, it is not discussed further. Connection management within the confines of an isochronous network for interactive multimedia is a newer technology (albeit with old roots) and deserves discussion.
Signalling for circuit and cell switching is best defined by the ISDN signalling standards (see, TR-NWT-000938, Network Transmission Interface and Performance Specification Supporting Integrated Digital Services Network (ISDN), Bellcore Technical Reference, Issue 1, (August 1990)), isoEthernet(copyright) signalling (see, IEEE Proposed Standard 802.9a, xe2x80x9cIsochronous services with Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Media Access Control (MAC) servicexe2x80x9d, (December 1994)) and ATM signalling (see, ATM Forum, xe2x80x9cATM User-Network Interface Specification Version 3.0xe2x80x9d, (September 1993) and ITU-T Recommendation Q.293, xe2x80x9cGeneric Concepts for the Support of Multipoint and Multiconnection Callsxe2x80x9d; (1993)). Historically, isochronous networks carry the signalling channel as an isochronous channel. Nevertheless, the signalling function can be shown to be better suited to a packet channel. A hub/routing function is the ideal location to perform the bridging between an isochronous signalling channel and a packet signalling channel. The natural packet protocol choice for a signalling channel is an Internet Protocol (xe2x80x9cIETF IPxe2x80x9d). Available on most LAN networks, as well as global routing capability, IP greatly enhances the signalling requirement of interactive multimedia.
Feature management consists of the management of those features provided by the private and public network for interactivity purposes. The PBX is followed as a model for interactive multimedia features. The following Table VI summarizes some of the more common features.
The third of the fundamental integration issues is interoperability. An interactive multimedia system by nature implies interoperability, because a multimedia network as envisioned is too large and far-flung to employ the equipment of only a single supplier. Therefore, standards must be established that allow equipment from different suppliers to interact smoothly. To this end, interoperability must extend to transport mechanisms, signalling and compression standards.
There are certain existing communication technologies that must be supported and others that are used. A truly interoperable interactive multimedia system should guarantee that the physical and logical interfaces of each component adheres to a standard. Prior to 1992, this would have been almost impossible. The present day affords the opportunity to evolve the proprietary telephony of the PBX and the proprietary video of the video conferencing systems into standards-based systems in the same manner that the data systems evolved from proprietary mainframes to the standards-based LAN systems of today. The following Table VII summarizes the required standards of interoperability.
In addition to the standards required for communications, there are other specifications relating to application programming interfaces for terminal and server control:. These include Microsoft(copyright) Telephony Application Programming Interface (xe2x80x9cTAPI(copyright)xe2x80x9d), Novell(copyright) Telephony Service Application Programming Interface (xe2x80x9cTSAPI(copyright)xe2x80x9d) and Microsoft(copyright) Open DataBase Connectivity (xe2x80x9cODBC(copyright)xe2x80x9d).
Having now set the stage with a discussion of general issues concerning multimedia systems, more specific design issues may now be discussed. The specific design issue of concern is provision of signalling within a private network or a hybrid network and a method to accomplish the signalling function between stations or nodes in the network.
Traditionally, isochronous devices such as telephones and video conferencing equipment have signalled in-band. xe2x80x9cIn-band,xe2x80x9d in traditional telephony, is defined as use of the same physical path for signalling and user information, such as voice, circuit mode and video data. In contrast, ISDN employs a D-channel, that, although carried over the same physical medium as the B-channels, is logically regarded as a separate channel. In the telephony world, this is defined as xe2x80x9cout-of-bandxe2x80x9d signalling.
However, since signalling services are intermittent processes, it is not necessary to perform this signalling within an isochronous channel. In fact, there is great benefit to be achieved by performing this signalling over a packet service or medium.
There are several key advantages to signalling over a packet service including, but not limited to, backbone signalling with simple circuit connectivity, routing, remote control, multicasting, and other operational benefits. Moreover, one of the advantageous aspects of using such signalling is the separation of the call control process from the circuit connection process. Because these two processes are implicitly separate, simplicity is achieved in call control through unknown networks. By establishing a data link between endpoints independent of the circuit connection, all feature management is transparently achieved. This is an absolutely essential feature for xe2x80x9cwork-at-homexe2x80x9d and for similar applications that traverse the public network. However, there are limitations, such as the bridging function between the isochronous signalling channel and the packet channel, unencountered in current signalling technology, that must be addressed before such signalling is commercially viable.
In further support of packet-based signalling, as the size and complexity of modern private and hybrid private/public networks increase, the mechanisms for communication of signalling information from one node to another become increasingly cumbersome and/or expensive. The simplest signalling network is a fully-webbed net in which each node has a direct connection to every other node in the network. This becomes prohibitively expensive as the number of nodes increases. The number of connections needed is equal to (n(nxe2x88x921))/2, where n is the number of nodes. If the network is configured to use fewer inter-nodal signalling paths, the complexity of the network topology increases significantly as the number of nodes increases. Modern packet technology allows for the establishment of multiple virtual connections without requiring full webbing of the physical connections. The problem is to develop a process for using this capability and applying it to private network signalling procedures such as QSIG.
Accordingly, what is needed in the art is a signalling subsystem and method that accomplishes the hub/routing/bridging functions between the isochronous signalling channel and the packet channel. Furthermore, what is needed in the art is a system for allowing the establishment of separate virtual connections within the context of conventional packet network topologies to provide a virtual signalling path from every node to every other node within a private network without requiring multiple physical connections for each node.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a system, employing hubs and bridges, for cross-translating telephony and computer network protocols. This cross-translating allows, in one significant aspect, packet-based signalling, significantly enhancing the bandwidth of signalling channels (e.g. 16/64 kbps D-channels verses 10 Mbps packet) and simplicity of communication (e.g. n physical connections verses n(nxe2x88x921) physical connections).
In the attainment of the foregoing primary object, the present invention, in one aspect, provides a system private network signalling message over a packet network. The system comprises: (1) an encapsulation circuit, coupled to a transmitting user station, capable of receiving the private network signalling message from the transmitting user station, the encapsulating circuit encapsulating the signalling message within, and adding source and destination addresses to, a routable protocol frame, the source and destination addresses corresponding to addresses of the transmitting user station and a particular receiving user station, the encapsulation circuit queuing the routable protocol frame for transmission over the packet network and (2) a de-encapsulation circuit, coupled to the particular receiving user station, capable of receiving the routable protocol frame, the de-encapsulation circuit extracting the signalling message from the routable protocol frame, the packet network thereby simulating a point-to-point connection between the transmitting and particular receiving user stations to effect node-to-node private, network signalling therebetween.
Thus, this aspect of present invention allows private network signalling to be routed over a packet network. The signalling messages, designed for node-to-node isochronous communication, are encapsulated into packets, allowing the packet network to route the encapsulated messages as though they are simply computer data. Fundamentally, the present invention allows a shared packet network backbone to simulate a web of discrete node to-node signalling connections.
In a preferred embodiment of this aspect of the present invention, the routable protocol frame is a User Datagram Protocol/Internet Protocol (xe2x80x9cUDP/IPxe2x80x9d) frame.
Those of skill in the art will understand that the present invention is applicable to any routable protocol frame. However, as will be shown, UDP/IP is flexible and enjoys wide acceptance as a standard for routing packets.
In a preferred embodiment of this aspect of the present invention, the private network signalling message is a Q.921 framed Q.931 signalling message. A Q.931 extension, or xe2x80x9cQSIGxe2x80x9d, signalling message is established at the network level between switching nodes in the system of the present invention.
Those of skill in the art are familiar with the substance and advantages of Q.921, Q.931 and QSIG signalling but also understand that other, known signalling standards are within the scope of the present invention.
In a preferred embodiment of this aspect of the present invention, the packet network comprises redundant backbones coupling the encapsulation circuit and the de-encapsulation circuit.
One of the hallmarks of a well-designed multimedia system is reliability. The present invention, in this preferred embodiment, employs redundancy often found in communication networks to enhance signalling reliability. By providing redundant backbones, the present invention in effect provides redundant node-to-node signalling webs.
In a preferred embodiment of this aspect of the present invention, the transmitting user station is capable of creating a user information path via an isochronous channel, the isochronous channel created on an isochronous network selected from the group consisting of: (1) an ATM network and (2) a Public Switched Digital Network (xe2x80x9cPSDNxe2x80x9d). Thus, the present invention preferably provides for out-of-circuit signalling wherein the signalling and call processing are handled over the packet network and the user information path, carrying the substantive data, is handled in a dedicated isochronous channel over the isochronous network. Again, xe2x80x9cin-band,xe2x80x9d for the purposes of the present invention, is defined as use of the same physical path for signalling and user information, such as voice, circuit mode and video data. xe2x80x9cIn-circuit, out-of-bandxe2x80x9d is defined, for purposes of the present invention, as signalling that, although carried over the same physical medium as the user information path, is logically regarded as a separate channel. xe2x80x9cOut-of-circuitxe2x80x9d signalling is defined as signalling that traverses a completely different physical circuit than does the user information path.
In a preferred embodiment of this aspect of the present invention, the particular receiving user station is coupled to a second encapsulation circuit and said transmitting user station is coupled to a second de-encapsulation circuit, the particular receiving user station thereby capable of transmitting a subsequent signalling message to the transmitting user station in response to receipt of the signalling message from the transmitting user station. Thus, the present invention provides for bi-directional communication of signalling messages over the packet network.
In a preferred embodiment of this aspect of the present invention, the packet network is free of transit nodes. Those of skill in the art recognize that private network signalling protocols, such as Q.931, commonly provide for intermediate transit nodes for both signalling and information transport. Such nodes, while necessary in a traditional webbed network introduce transmission delays and complicate the network. Since the present invention adapts such signalling to packet networks, the need for signalling transit nodes is eliminated, thereby simplifying communication of signalling messages.
In a preferred embodiment of this aspect of the present invention, a user information path coupling the transmitting and receiving user stations is free of private network signalling messages. While the present invention may allow for both in-band and out-of-band signalling, the present invention is preferably directed toward out-of-band signalling, wherein signalling is communicated along a separate path from user information.
In a preferred embodiment of this aspect of the present invention, the packet network comprises a plurality of encapsulation circuit/de-encapsulation (xe2x80x9cE/Dxe2x80x9d) circuit pairs, each of the pairs functioning as an addressable node on the packet network.
In a preferred embodiment of this aspect of the present invention, the encapsulation and de-encapsulation circuits comprise sequences of executable software instructions. Those of skill in the art will recognize, however, that the encapsulation and de-encapsulation circuits can be embodied in discrete or integrated hardware, or as firmware associated with a programmable device.
In the attainment of the foregoing primary object, the present invention, in another aspect, provides a bridge for communicating a MAC layer frame over an isochronous channel, comprising: (1) a frame reception and storage circuit coupled to a nonisochronous network, the frame reception and storage circuit capable of receiving the MAC layer frame from the nonisochronous network and storing the MAC layer frame in the frame reception and storage circuit and (2) a frame encapsulation circuit coupling the frame reception and storage circuit and the isochronous signalling channel, the frame encapsulating circuit capable of encapsulating the stored MAC layer frame into a first frame and queuing the first frame for transmission over the isochronous signalling channel. This aspect is directed, therefore, to transport of MAC layer packets over a private isochronous signalling channel, such as the D channel of an IEEE 802.9 link.
In a preferred embodiment of this aspect of the present invention, the MAC layer frame comprises a cyclical redundancy check (CRC), the frame encapsulation circuit stripping the CRC from the MAC layer frame. The CRC allows verification of the data in the MAC layer frame. This is not required for isochronous signalling channel transport; therefore, it is eliminated.
In a preferred embodiment of this aspect of the present invention, the frame encapsulation circuit is further capable of (a) negotiating a larger maximum frame size by generating and receiving transmit identification (xe2x80x9cXIDxe2x80x9d) messages over the isochronous signalling channel and (b), if the negotiating is unsuccessful, dividing the stored MAC layer frame into first and second segments, individually encapsulating the first and second segments into first and second frames, respectively, assigning a segment number to each of the first and second frames and queuing the first and second frames for transmission over the isochronous signalling channel. If the larger maximum size is received, the first and second frames may be larger. The larger frame size may eliminate the need to segment the MAC layer frame. If the larger size is not granted, segmentation becomes a more likely requirement. It is desirable to avoid segmentation whenever possible because of the added overhead involved (as will be described). However, some systems may not support a larger frame size. Thus, the present invention provides for segmentation to accommodate such systems.
In a preferred embodiment of this aspect of the present invention, the first and second frames each comprise an address field and a control field. In a related, preferred embodiment of this aspect of the present invention, the first and second frames are Q.921 Unacknowledged Information frames.
In a preferred embodiment of this aspect of the present invention, the frame encapsulation circuit is further capable of receiving third and fourth frames from the isochronous signalling channel and de-encapsulating and concatenating the third and fourth frames to form a MAC layer frame for transmission over the nonisochronous network. Thus, the present invention is bidirectional.
In a preferred embodiment of this aspect of the present invention, the nonisochronous network is an Ethernet(copyright) network. Ethernet(copyright) networks are widely used and well accepted. Those of skill in the art are familiar with other nonisochronous network topologies, such as Token Ring(copyright) by IBM, that are within the broad scope of the present invention.
In a preferred embodiment of this aspect of the present invention, the first and second frames each comprise last segment and current segment length fields. These field cooperate to provide the segmentation scheme. Each frame containing segmented data contains an indication of the length of the segment and whether it is the last frame of the sequence.
In a preferred embodiment of this aspect of the present invention, the first frame comprises a total MAC layer frame length field. This field thus gives an indication to the receiving device of the length of the MAC layer frame, useful for reconstruction purposes.
In a preferred embodiment of this aspect of the present invention, the MAC layer frame is an Ethernet(copyright) frame. Again, Ethernet(copyright) is a widely recognized standard for packet networking.
In the attainment of the foregoing primary object, the present invention, in yet another aspect, provides a bridge for communicating an isochronous signalling frame over a nonisochronous network, comprising: (1) a frame reception circuit coupled to an isochronous channel, the frame reception circuit capable of receiving the isochronous signalling frame from a subordinate device via the isochronous channel and (2) a frame encapsulation circuit coupling the frame reception circuit and the nonisochronous network, the frame encapsulating circuit capable of encapsulating the isochronous signalling frame into a routable protocol frame and queuing the routable protocol frame for transmission over the nonisochronous network to a destination device, the nonisochronous network thereby capable of simulating a point-to-point connection between the subordinate device and the destination device.
In particular, this aspect allows a packet network to support multiple servers and multimedia hubs, thereby enhancing the scalability and reliability of multimedia systems. The destination device, acting as a server or multimedia manager, handles top-level allocation of isochronous resources. Signalling messages, generated by the subordinate device, can be routed via the nonisochronous, packet network, to the destination device.
In a preferred embodiment of this aspect of the present invention, the routable protocol is a UDP/IP frame, the frame encapsulation circuit further capable of setting a source address field of the routable protocol frame equal to an address of the bridge and setting a destination address field equal to an address of the destination device. As previously described, UDP/IP is a recognized standard advantageously applicable to the present invention.
In a preferred embodiment of this aspect of the present invention, the frame encapsulation circuit is further capable of receiving a subsequent routable protocol frame from the destination device via the nonisochronous network, the encapsulation circuit de-encapsulating a subsequent isochronous signalling frame from the routable protocol frame and queuing the isochronous signalling frame for transmission over the isochronous channel. Thus, the present invention preferably provides bidirectional communication.
In a preferred embodiment of this aspect of the present invention, the routable protocol is a UDP/IP frame, the frame encapsulation circuit further capable of setting a UDP source port equal to a link number of the subordinate device. In a related preferred embodiment of this aspect of the present invention, the frame encapsulation circuit is further capable of setting a UDP destination port equal to a well-known call processing port. As will be described, source and destination ports are used to direct the frame through the network.
In a preferred embodiment of this aspect of the present invention, the isochronous signalling frame is a Q.921 signalling frame. As previously described, such frames ate well known in the art.
In a preferred embodiment of this aspect of the present invention, the nonisochronous network is an Ethernet(copyright) network. In a related, preferred embodiment of this aspect of the present invention, the frame reception circuit is further capable of validating a frame check sequence number of the isochronous signalling frame.
In a preferred embodiment of this aspect of the present invention, the reception circuit is coupled to a plurality of subordinate devices via a plurality of isochronous channels. Thus, the reception circuit is preferably embodied in a hub that, in the context of a multimedia system, is a multimedia hub.
In a preferred embodiment of this aspect of the present invention, the nonisochronous network couples a plurality of bridges and destination devices, the nonisochronous network simulating a plurality of point-to-point is ochronous channels coupling the plurality of bridges and destination devices.
The present invention further provides methods of: (1) communicating a private network signalling message over a packet network, (2) communicating a Media Access Control (MAC) layer frame over an isochronous channel and (3) communicating an isochronous signalling frame over a nonisochronous network.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.